class UsernameConverter:
    regex = '[a-zA-Z0-9_-]{5,20}'
    def to_python(self, value):
        return str(value)
    def to_url(self, value):
        return str(value)

class MobileConcerter:
    regex = '1[3-9]\d{9}'
    def to_python(self, value):
        return int(value)
    def to_url(self, value):
        return str(value)